An oil well comprises an earth borehole which may be lined with casing or liner that is bonded to the earth formation with cement. Perforating of an Oil/Gas well refers to the process of punching holes through the casing or liner and into the surrounding reservoir with a perforating gun. The holes or perforations are formed in a desired reservoir zone to connect the reservoir with the interior of the casing or liner. Generally, a perforating gun comprises a tube or pipe containing a series of shaped charges which, when detonated, causes the perforations through the casing or liner. Several mechanisms are available for deploying perforating guns, including electric line, slickline, coiled tubing, and other tubing. Perforating guns may be triggered (fired) with a firing head.
Various methods have been used to set off perforating guns deployed by tubing. For example, several methods have been employed for triggering firing heads and examples of those methods include drop bar activation, over pressure commands, differential pressure commands, and pressure pulse commands. Pressure pulse commands may be used with electronic firing heads. According to other relatively new methods either ultra-low frequency electromagnetic or acoustical telemetry techniques have been used for communicating with an electronic firing head(s).